Case IH 520592-03 - BCM – Body Control Module (BCM): Mirror heater indicator Voltage Above Normal, or Shorted to High Source

The Body Control Module (BCM) has detected that the circuit controlling the mirror heater indicator light (usually built into the switch) is shorted to battery voltage (B+).

• MAGNUM AFS Connect
• Case IH Maxxum series (e.g., 110, 140)
• Case IH Puma series (e.g., 210)
• Case IH Magnum series
• Case IH Optum series

1. 1

   Verify the condition of the mirror heater fuse (10A Mini Red fuse F-012).

2. 2

   Disconnect the mirror heater switch. Turn the key ON and check if the fault code changes from FMI 03 (Short to B+) to FMI 05 (Open Circuit) to determine if the short is internal to the switch.

3. 3

   Inspect the 2-pin connection cables routing from the cab A-pillar/console to the exterior mirrors for pinched wires in the door hinge area or melted insulation.

4. 4

   With the switch disconnected and the tractor ON, use a multimeter to probe the indicator signal wire at the switch harness to see if it reads 12V (B+) when it shouldn't, indicating a short to power.

1. 1

   Power Down

   Turn off the ignition and disconnect the negative battery cable to prevent module damage.

2. 2

   Access the Switch Panel

   Carefully pry out the control unit panel where the mirror heater switch is located (often grouped with work lamps and rotating beacon switches).

3. 3

   Test the Switch

   Test the switch for internal continuity. If the internal indicator circuit is shorted directly to the 12V supply pin, the switch has failed internally.

4. 4

   Trace the Harness

   If the switch tests fine, trace the wiring harness back to the BCM. Repair any chafed wires that are bridging the indicator wire to a 12V power wire. Use heat-shrink tubing to seal the repair.

5. 5

   Reassembly & Timer Test

   Reconnect the switch and battery. Turn the ignition to position 2. Depress the mirror heater switch. Verify the indicator illuminates and that the BCM automatically switches the heater off after the programmed time (typically 5 to 10 minutes).

6. 6

   Clear Codes

   Use the diagnostic tool to clear the 520592-03 code from the BCM memory.